Yea, you have to be careful of something just because "it hardens." There are a lot of hard things that still are able to leach out dangerous chemicals or molecules even when hardened. The problem is made worse in that food is often moist or wet. Think about a bunch of beautiful tomato slices on a plate. There is water everywhere that is going into your mouth having touched and potentially dissolved or absorbed some harmful molecules from the plastic.

Just do what Eddie did, always ask the manufacturer if in doubt.